The roles of various bacterial and viral genes involved in M13 DNA replication will be investigated. Host mutants will include strains defective for the DNA G protein and the 5' 3' exonuclease of polymerase I. DNA structures made under non-permissive conditions will be characterized by ultracentrifugal analysis and electron microscopic examination. Further details of the physical map of M13 DNA will be obtained through restriction endonuclease analysis. Origins of DNA replication will be located relative to known sites in the viral DNA.